Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the bar is lower. The description adds two behaviors not in the annotations: result ordering (oldest first) and the fact that reading does not clear the unread count. It omits any pagination or truncation behavior for long histories.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two short sentences with the core purpose front-loaded and no filler. The second clause earns its place by disambiguating a side effect rather than merely restating readOnlyHint.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists, so return shape needn't be described, and annotations cover the safety profile. What's missing is behavior at the limit boundary (max 100) for long conversations — with ordering stated as oldest-first, an agent has no guidance on how to reach newer messages.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 50%: contact is well documented inline but limit only carries default/min/max. The phrase 'oldest first' does add real meaning to limit, implying the first N oldest messages rather than the latest N, but the description never states this trade-off explicitly or how to page further back.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States the specific verb and resource: texts exchanged with one number, returned oldest first. That scoping to a single number implicitly distinguishes it from list_conversations, but it never explicitly says how it differs from get_message or list_messages.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Clarifies the read-only nature and routes unread-clearing to mark_read, which is a genuine routing hint that resolves a common agent question ('will reading mark as read?'). It stops short of naming exclusions against get_message, list_messages, or wait_for_reply.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.